Heyerdahl's research focuses on inferring the drivers of spatial and temporal variation in fire regimes over the past several centuries using tree rings and modern fire records. These drivers include climate, forest type, topography, and land use.
This research impacts both forest management and our understanding of basic forest and fire ecology. The National Fire Plan, the Federal Wildland Fire Management Policy, and the Forest Service's Cohesive Strategy clearly identify the need to restore frequent-fire forests by treating fuel. Knowledge of past fire regimes, how and why they varied across space, and how they affected forest structure and composition provides a basis for prescribing fuel treatments that mimic the effects of past fires, while knowledge of the climate forcing of extreme fire years provides a basis for scheduling such treatments. Spatially explicit reconstructions of fire regimes can be used to identify fundamental properties of those regimes, such as the scaling properties of fire frequency. Knowledge about the drivers of spatial and temporal variation in historical fire regimes is used by other scientists to parameterize, and validate simulation models, for example to predict the effects of climate change on future fire regimes. Anticipating the effects of climate change on future fire requires that we understand the effects of climate variation on past fires using tree rings and also that we bridge the past and the present by identifying the climate drivers of 20th-century fires from written archival records.